The already soggy Bay Area will be hit by a powerful storm this weekend that could deliver some of the worst flooding in years to California, especially at Yosemite National Park, where the Merced River is expected to surge to dangerous and potentially record-breaking levels.

In the Bay Area, the storm should dump up to 5 inches of rain starting Friday evening, and more than twice that amount in the Santa Cruz Mountains, wreaking havoc on the region’s roads and infrastructure, according to weather forecasters.

“This system over the weekend will be like a water hose from the Pacific Ocean,” said meteorologist Brian Mejia of the National Weather Service. The service is regularly updating its forecasts here.

The flooding in certain communities could be severe. On Wednesday, water was already inundating low-lying areas in Sonoma County and Santa Cruz County. By Sunday, the Russian River is expected to reach about 29 feet in Guerneville, nearing the flood stage of 32 feet, and waterways all over the Bay Area will be swollen. San Jose’s Guadalupe River could threaten to flood as well.

But nowhere is the flood potential more dramatic than Yosemite Valley. The National Park Service is closely monitoring the Merced River, which the National Atmospheric and Oceanic Administration is predicting could rise as high as 23 feet this weekend at Pohomo Bridge. That would be more than double the flood stage, threatening a record set in January 1997, when historic flooding caused widespread damage to roads, utilities and campgrounds.

Park officials are warning visitors that Yosemite may need to close in coming days, depending on how high the river crests. The park service was expected to make further announcements as early as Thursday.

“We’re working to be proactive to ensure employee and park visitor safety,” said National Park Service spokeswoman Jamie Richards.

This weekend’s storm will dump a lot more water on a saturated region. So far, North Bay counties and the Santa Cruz Mountains have received the greatest amount of rain over the past two days, with some peaks in Marin County recording 4 inches of precipitation, according to the National Weather Service. The steady rain took down trees, triggered mudslides in West Marin and Santa Cruz counties, and left an estimated 1,600 Bay Area residents without power Wednesday.

Wednesday’s drizzle was expected to let up by Thursday and be replaced by a cold front that could send nighttime temperatures into the low 30s, according to the National Weather Service. Concord, Livermore and parts of the North Bay will see temperatures plummet below freezing starting Thursday evening, with icy roads expected Friday morning.

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By Friday evening, heavy rain is expected to return, pushed by an atmospheric river coming off the Pacific Ocean. The storm, which will last through Monday, is expected to flood underpasses, creeks and rivers and could endanger unlucky or unsuspecting motorists.

“Sunday is going to be the big ticket day after the water works its way down through the watershed,” said Mark Strudley, a hydrologist with the National Weather Service.

The Santa Cruz Mountains often bear the brunt of winter storms. John Presleigh, director of public works for Santa Cruz County, said the San Lorenzo Valley received 7-8 inches of rain Tuesday and Wednesday, with another 12 inches anticipated this weekend.

With hillsides already saturated with rain, mudslides could be widespread. Crews were busy Wednesday preparing for the storm and responding to 11 road closures, including a slide that blocked San Jose Soquel Road near Hester Creek Road.

“We’re doing everything we can at this point, but Mother Nature is coming at us,” Presleigh said. “It looks like we’re going to get dumped on.”

Presleigh encouraged rural residents to clean out their culverts and prepare to hunker down. And he urged mountain motorists to drive slowly and carefully and watch out for road crews.

Conditions will be especially treacherous in areas that were scorched this fall by the Loma fire, which burned 4,474 acres in rural Santa Clara County, and the Soberanes fire, an inferno that charred 132,127 acres in the coastal mountains of Monterey County. Burn scars that lack vegetation are particularly vulnerable to mudslides.

Down along San Francisco Bay, public works officials in low-lying regions are keeping a close eye on flood-prone communities.

At Le Mar Trailer Park in Redwood City, which was hit by severe flooding during the “superstorm” of December 2014, resident Denise Roldan said that, although she is concerned about the heavy rainfall expected this weekend, she’s also grown accustomed to flooding problems during nearly three decades at the park on East Bayshore Road.

The trailer she shares with her longtime partner, Bert Coil, sustained several thousand dollars of damage during the 2014 flood. But the situation could be worse, said Coil, thinking of places in the Midwest that get flattened by tornadoes.

“All you do is wake up and hope you don’t have to go swimming,” said Coil, 58.

Farther up the Peninsula, the storm will have the full attention of officials in Pacifica, who last month declared they will demolish a clifftop apartment building on Esplanade Avenue that was evacuated last winter.

In the North Bay, Marin County Fire officials were also bracing for the big storm, beefing up staffing at a command center in West Marin and getting water rescue teams ready to help stranded motorists, said Battalion Chief Bret McTigue.

“If the rains pan out as expected, we expect all of our creeks to be at flood advisory stage,” McTigue said. “We advise everyone to not cross roadways that have standing water and prepare for the winter storm with sandbags, a source of light and heat in case there are power outages.”

Karina Ioffee covers the city of Richmond and West Contra Costa County. She has been a reporter for 15 years and has won numerous awards for her work, including from the Overseas Press Club. She speaks Spanish and Russian and is a former competitive gymnast. When not working, she likes to do yoga, cycle and dance.